Method for the softening of tough mushrooms

ABSTRACT

A process for softening tough mushrooms or parts thereof by subjecting the mushrooms to an enzymatic treatment. The disclosed process makes possible the attainment of soft, edible mushroom fruit bodies having an agreeable consistency and good flavor. The process involves cleaning the mushroom material and subjecting the cleaned mushroom material to aerobic or anaerobic incubation in a sour solution having a pH value ranging from 3 to 5.5 and a salt percentage ranging from 0.02 to 0.5 mole. Glucanase or chitinase may also be added to the solution. Incubation is carried out at a temperature between 20° C. to 55° C. for a period ranging from 12 hours to 5 days. After incubation, the material is boiled and packed at a reduced pressure. The process makes possible the preservation of flavorful, edible mushroom material independent of mushroom harvesting seasons.

BACKGROUND OF THE INVENTION

All pleurotos kinds which are cultivated have tough stems which accountfor approximately 20 to 25% of the production and which are thrown awayas waste. The fruit body spoils easily. They get tougher through storagein a refrigerator. Freezing is only suitable after previous blanching.Dried mushrooms become like rubber after dehydration (TR. Gormely and F.O'Riordian, Lebensm.-Wiss. u. Techn., Bd.9 (1976) S 75-78). All otherapplied means of conservation require a more or less extensive heattreatment, but each heat treatment (blanching, cooking, sterilization,drying) increases the toughness of the fruit body and especially that ofthe stems.

Fermentation of the mushrooms was repeatedly tried in the past. Apartfrom the long duration, the adding of sugar and the lack of controllingthe fermentation, this method was disadvantageous because the materialhad to be blanched. (W. Botticher, Technology der Pilzverwertung, VerlagEugen Ulmer, 1974). Quick silaging (R. Kselig, Ceska, mykol, 10, 1956,p. 190) required previous boiling of the mushrooms for 10 to 15 minutes.Without sterilization the product lasted for only 2 to 3 days.Therefore, the previously used methods of conservation are not suitable.

SUMMARY OF THE INVENTION

The object of the invention is to provide soft, eatable mushrooms orparts of them, as well as a method to produce them from tough fruitbodies or parts of them unsuitable for consumption. Another object ofthe invention is to give the tough mushroom material a pleasantconsistency and good taste.

Another objective of the invention is the conservation of the mushroommaterial without risking deterioration of consistency.

Yet another object is to render the preservation of the mushroommaterial independent of the harvest periods.

The solution to the inventive object is based on the development of anincubation method by using added enzymes or enzymes of the mushroomsthemselves (glucanases and chitinases).

The invention hence relates to the object as characterized in the patentclaims.

The method of the invention allows the conversion of fresh ordifferently long frozen or heat-treated tough mushroom bodies or partsthereof into a product having a soft, very pleasant consistency,appealing to the eye and having an appetizing aroma.

Moreover, the method allows the preservation of the mushroom productwith simple means.

The method of the invention entails the following advantages:

1. Previously, mushroom stems had to be discarded because of theirtoughness. Due to this novel method it is possible for the first time,to make them usable for human consumption.

2. The new method provides tough mushroom fruit bodies and/or partsthereof with a pleasant soft consistency.

3. Any preservation method previously used required heat treatment whichincreases toughness of the mushrooms and parts theirof, and incurscosts. With the inventive method raw mushroom material can be used.

4. Mushroom material that has become tough due to heat treatment canalso be provided with a pleasant consistency due to the novel method.

5. Mushroom material that has been frozen for any period of time canalso be used with the inventive method since freezing does not affectthe enzyme activities.

6. The inventive method allows heat treatment of the mushroom materialeven after the latter has become soft, without deteriorating theconsistency.

7. Toughening of the mushroom material by heat treatment can beprevented by subjecting it to a short pre-treatment according to theinventive method.

8. The inventive method renders preservation independent of theharvesting periods since the mushroom material used can be stored in adeep-frozen condition for any period of time.

9. The inventive method also imparts a good preservation characteristicto the mushroom product.

10. The inventive method yields a mushroom product whose flavor can bevaried according to the consumer's wishes.

11. The inventive method requires only a little expenditure in energy,time and costs.

The inventive method requires 2 essential steps:

(A) Preparation of the mushroom material

(B) Softening of the mushroom material through incubation.

Incubation can be followed by the following steps:

(C) Seasoning

(D) boiling and packaging.

DETAILED DESCRIPTION

The individual steps of the inventive method are explained in detail inthe following:

(A) Preparation of the mushroom material

Starting materials include freshly harvested mushrooms, tough mushroomfruit bodies or their parts, for instance pleurotus types, or materialfrozen at -2° to -40° C. that has been stored up to two years, ormaterial that became tough through heat treatment. The mushroom fruitbodies can be processed unwashed when the cultivation method providesclean material, otherwise they must be cleaned and washed. The mushroomfruit bodies are put into containers of any size, in whole or in bitsand are then covered with the sour solution.

(B) Softening of the material

An acid solution in the range of pH 3 to pH 5.5 (preferably pH4) is usedwhich may have a salt content of a molarity of 0.02 to 0.5 m (preferably0.1 to 0.15). The fruit bodies or their parts get soft at temperaturesof 20° to 55° C. (preferably 35° to 40°) after an aerobic or anaerobicincubation of 12 hours to 10 days. Especially buffer solutions can beused as acid solution, for instance acetic acid, citric acid, lacticacid or sour curdled milk from fermentive lactic fermentation. Enzymesare added to fruit bodies of mushroom strains which soften too slowlybecause they do not contain sufficient glucanases and chitinases, or tofruit bodies which have become tough due to heat treatment, such enzymesbeing added in the form of

(a) enzyme-rich pieces of fruit body;

(b) solutions of enzyme-rich pieces of fruit bodies after the softeningprocess;

(c) juice of enzyme-rich fruit bodies after storage in frozen condition;

(d) watery extracts made from comminuted enzyme-rich fresh or PG,5frozen fruit bodies;

(e) enzymes (glucanases and chitinases) which were separated with theorganic solvents mixable with water or with high salt concentrationsfrom the solutions (b)-(d);

(f) enzymes corresponding to (e), which were more or less cleaned.

(C) Seasoning

The softened mushroom product can be spiced with various seasonings asthey are commonly used in the production of mushroom dishes, whereby anaddition of table salt is possible even before the enzyme treatment.

(D) Cooking and packaging

In order to prevent the growth of mold and yeast, the finished productis boiled shortly (5 to 10 min) and closed under reduced pressure.

In order to check the softening of the mushroom fruit bodies or theirparts the following consistence measurement was carried out:

The mushroom piece to be tested was placed in an upside-down cover of apetri dish (5 cm diameter) and the bottom of the dish was loaded withweights of 100 g (=300 Pa) up to 3 kg (=9000 Pa). Pieces which could becrushed up to 4500 Pa were defined as "soft".

The following examples illustrate the inventive method (examples 1-7 forsteps (A) and (B), examples 8 and 9 for steps (C) and (D)):

EXAMPLE 1

(A) Fresh stems of pleurotus ostreatus, Symycel 3004 strain, were usedas material. The stems were cleaned, cut into pieces of roughly 1 g inweight, and filled into either small containers (=k, test tubes 25×250mm) or medium-sized containers (=m, 1/4 l screw cover glasses) or inlarge containers (=g, 1 l canning glasses).

(B) The prepared material was covered with 0.15 m lactic acid buffer (a)or with 0.15 m citric acid buffer (b), both pH 4, and incubated for 48 hat 40° C. (see table 1).

                  TABLE 1                                                         ______________________________________                                        Softening of fresh, enzyme-rich material in                                   citric acid or lactic acid buffer                                             % soft pieces after      container                                            24 h      48 h       buffer       size                                        ______________________________________                                        100       100        (a)         k                                            90        100        (a)         m                                            100       100        (a)         g                                            90        100        (b)         k                                            90        100        (b)         m                                            100       100        (b)         g                                            ______________________________________                                    

EXAMPLE 2

(A) Stems of Pl.ostreatus, Somycel 3004 were used as material, which hadbeen stored at -18° C. for different periods of time. The material wasprepared as in example 1.

(B) The stem pieces were covered with 0.15 m citric acid buffer of 4 pHand incubated for 24 hours or 48 hours at 40° C. (see Table 2).

EXAMPLE 3

(A) Fresh stems from pleurotus ostreatus, Somycel 3004 or Floridastrain, which had been stored for 3 month at -18° C., were used asmaterial. The material was prepared as in example 1 and subsequentlyheated to 121° C. for 5 minutes so that all softening enzymes weredestroyed.

(B) After that, fresh pieces of pleurotus ostretus, Somycel 3004 strain,were added the ratio of 1:1, covered with lactic acid buffer of pH 4 andincubated at 40° C. for three days (see table 3).

                  TABLE 2                                                         ______________________________________                                        Softening of enzyme-rich stem pieces which were stored                        in lactic acid buffer at -18° C. for different periods of time         % soft pieces after                                                                               freezing time                                                                              container                                    24 h     48 h       (month)      size                                         ______________________________________                                        90       100        1            k                                            100      100        1            m                                            90       100        1            g                                            100      100        3            k                                            100      100        3            m                                            100      100        3            g                                            100      100        6            k                                            80       100        6            m                                            90       100        6            g                                            100      100        9            k                                            80       100        9            g                                            90       100        12           k                                            90       100        12           g                                            ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Softening of heat-treated stem pieces by addition of                          fresh enzyme-rich stem pieces                                                                % soft pieces of                                                       Container                                                                              Somycel 3004                                                                              Florida                                          Treatment size       fresh   frozen                                                                              fresh frozen                               ______________________________________                                                  k          0       0     0     0                                    heated to m          0       0     0     0                                    121° C.                                                                          g          0       0     0     0                                    heated to k          100     100   100   100                                  121° C. plus                                                                     m          100     100   100   100                                  fresh stem                                                                              g          100     100   100   100                                  pieces                                                                        ______________________________________                                    

EXAMPLE 4

(A) The material was prepared in the same manner as in Example 3.

(B) The enzyme-containing buffer solution was separated by filteringfrom the material that was treated for 48 hours as described in Examples1 and 2, and then added to the prepared material. It was incubated for 5days at 40° C. (see table 4).

                  TABLE 4                                                         ______________________________________                                        Softening of heat-treated stem pieces by adding an                            enzyme-containing material buffer solution                                                   % soft pieces of                                                       Container                                                                              Somycel 3004                                                                              Florida                                          Treatment size       fresh   frozen                                                                              fresh frozen                               ______________________________________                                                  k          0       0     0     0                                    heated to m          0       0     0     0                                    121° C.                                                                          g          0       0     0     0                                    heated to k          100     100   100   100                                  121° C. +                                                                        m          100     100   100   100                                  solution from                                                                           g          100     100   100   100                                  example 1                                                                     heated to k          100     100   100   100                                  121° C. +                                                                        m          100     100   100   100                                  solution from                                                                           g          100     100   100   100                                  example 2                                                                     ______________________________________                                    

EXAMPLE 5

(A) Material and preparation as in example 3

(B) Stems of Pl.ostreatus, Somycel 3004 which were frozen at -18° C. fordifferent periods, were squeezed after thawing to 2° C. The juice wastitrated to pH 4 with 1 m citric acid, and filtered at sterileconditions. The solution was added to the prepared material. It was thenincubated for 5 days at 40° C. (see Table 5).

                  TABLE 5                                                         ______________________________________                                         Softening of heat-treated stem pieces                                        by adding enzyme-containing                                                                    % soft pieces of                                                       Container                                                                              Somycel 3004                                                                             Florida                                         Treatment   size       fresh  frozen                                                                              fresh                                                                              frozen                               ______________________________________                                        Reference:  k          0      0     0    0                                    heated to   m          0      0     0    0                                    121° C.                                                                            g          0      0     0    0                                    heated to   k          100    100   100  100                                  121° C. + squeezed                                                                 m          100    100   100  100                                  juice       g          100    100   100  100                                  ______________________________________                                    

EXAMPLE 6

(A) Material and preparation as in example 3

(B) Both fresh and frozen stems of Pl.ostreatus, Somycel 3004 strainwere cut into pieces and put into a Waring Blender, for homogenizationwith acetic acid buffer at pH 4 while being cooled, this proceduretaking 10 minutes, then it was centrifuged. The resulting enzyme-richsolution was added to the prepared material. It was incubated for 5 daysat 40° C.

                  TABLE 6                                                         ______________________________________                                        Softening of heat-treated stem pieces by adding watery                        extracts from enzyme-rich material                                                   % soft pieces of                                                              Somycel 3004  Florida                                                  Treatment                                                                              fresh     frozen    fresh   frozen                                   ______________________________________                                        Reference:                                                                             0         0         0       0                                        heated to                                                                     121° C.                                                                heated to                                                                              100       100       100     100                                      121° C. +                                                              extract                                                                       from fresh                                                                    stems                                                                         heated to                                                                              100       100       100     100                                      121° C. +                                                              extract from                                                                  frozen stems                                                                  ______________________________________                                    

EXAMPLE 7

(A) Only frozen stems of Pl.ostreatus, Somycel 3004 were used asmaterial, which were prepared as in example 3, except that only smallcontainers were used.

(B) Enzymes were extracted from enzyme-rich solutions like buffersolutions from softened stems according to example 1 and 2, squeezedjuices, and watery extracts from enzyme-rich stems according to example5 and 6:

(a) The cooled solution was mixed with acetone at a ratio of 1:4. Theresulting precipitation was centrifuged off in the cold and washed twicewith cold acetone and once with cold diethylether.

(b) Ammonium sulfate was added to the cooled solution to a 80%saturation, the precipitate was centrifuged off and washed twice with80% ammonium sulfate. The centrifuged product was mised with crystallineammonium sulfate to a 100% saturation. The resulting precipatate wasalso centrifuged off and washed twice with 100%--i.e.saturated--ammonium sulfate solution. The precipitated enzymes from (a)and (b) were either used directly or frozen at -18° C. or freeze-dried.

Prior to being used, the enzyme preparation was separated from the pH4in a 0.15 m citric acid buffer, so that an enzyme solution was obtainedwhich was ten times more concentrated than the original solution. Onepart of this solution was used directly, another part was first dialyzedwith a buffer solution at 2° C.-4° C. for 8 hours. The sour enzymesolution was added to the prepared stem pieces and incubated for threedays at 40° C.

                  TABLE 7                                                         ______________________________________                                        Softening of heat-treated stem pieces with enzyme                             preparations                                                                  Precipitation of                                                                           Application of                                                                              % soft stems of                                    the enzyme with                                                                            the enzyme    Somycel 3004                                       ______________________________________                                        acetone      direct        100                                                acetone      frozen        100                                                acetone      freeze-dried  100                                                80% (NH.sub.4).sub.2 SO.sub.4                                                              direct        100                                                80% (NH.sub.4).sub.2 SO.sub.4                                                              frozen        100                                                80% (NH.sub.4).sub.2 SO.sub.4                                                              freeze-dried  100                                                100% (NH.sub.4).sub.2 SO.sub.4                                                             direct        100                                                100% (NH.sub.4).sub.2 SO.sub.4                                                             frozen        100                                                100% (NH.sub.4).sub.2 SO.sub.4                                                             freeze-dried  100                                                ______________________________________                                    

The results are the same for unwashed and dialyzed enzymes.

The proteins which were extracted with the ammonium sulfate were testedfor glucanase and chitinase activity. Taken as the substrate for thetests was (according to the instructions by J. G. H. Wessel (Wentia, Bd.13 (1965), p. 1-113) isolated R-glucane and colloidal chitin which wasproduced from chitin in accordance with the instructions by L. R. Bergerand D. M. Reynolds (Biochim. Biophys. Acta, Bd. 29 (1958).

The glucose determination was done with the Merck-o-test blood sugar(Merck No. 3306) glucosamine determination with Indol according to Z.DISCHE (in Glick, Methods of biochemical analysis, Vol. 2, p. 353,Interscience Publishers, New York, 1955), after one hour of the enzymestaking an influence on the substrate (see table 8).

                  TABLE 8                                                         ______________________________________                                        Protein extracted                                                                         Glucose from                                                                             Glucose from                                                                             Glucose from                                with        R-glucane  S-glucane  Chitin                                      ______________________________________                                        80% (NH.sub.4).sub.2 SO.sub.4                                                             +++         +         ++                                          100% (NH.sub.4).sub.2 SO.sub.4                                                            ++         (+)        ++                                          ______________________________________                                         +++:strong reaction                                                           ++:distinct reaction                                                          :weak reaction                                                                (+):very weak reaction                                                   

The methods applied in Examples 1 to 7 were repeated with lactic acidwhich occurs during lactic fermentation. Substantially the same resultsare obtained.

EXAMPLE 8

The softened stems from example 1 were seasoned with salt, pepper,onions and bay leaves, cooked for 5 minutes and vacuum-packed.

EXAMPLE 9

The softened stems from example 2 were seasoned with salt, sugar, peeledhorse-radish and some cloves, boiled for ten minutes and thenvacuum-packed.

I claim:
 1. A method for treating tough mushrooms, comprising the stepsof:placing cleaned mushroom material within a container; adding asolution to said mushroom material within said container, said solutioncomprising a liquid having a pH of from 3 to 5.5 and having a saltpercentage of 0.02 to 0.5 molar; and allowing said mushroom material andsaid solution to interact in the presence of an enzyme selected from thegroup consisting of glucanase and chitinase at a temperature of from 20°C. to 55° C. for a period ranging from 12 hours to 5 days said enzymebeing added to said solution in an amount in excess of what is naturallyin said mushroom material, said amount of enzyme being sufficient toincrease the softening of said mushroom material.
 2. A method as claimedin claim 1 wherein said liquid having a pH ranging from 3 to 5.5 isselected from the group consisting of acetic acid, citric acid, lacticacid, or sour curdled milk from fermented lactic fermentation.
 3. Amethod as claimed in claim 2 wherein the pH of said liquid isapproximately
 4. 4. A method as claimed in claim 1, further comprisingthe steps of boiling said solution containing said mushroom material;andpackaging said mushroom material under reduced pressure.